PeepShow is the best British comedy at the moment (thought it's quality is alas, rapidly declining).
I also think Young Ones, Red Dwarf, Spaced, Blackadder, Father Ted - the list goes on. I find American comedy very hard to get into, the set up and punches are too flagged up in my opinion, though there are often some good lines in them.
Oh yeah! And My Parents Are Aliens, that was a children's sitcom, that was great.
Oh, Oh, and The Goons, Spike Milligan was ace.